Easy-to-obtain assault weapons, once banned under U.S. law, are a common thread connecting many of the deadliest mass shootings that have occurred in the past few years. Many gun violence experts believe that it's time to bring back the federal assault weapons ban — or at least something like it.

“You would see drastic reductions in what I call gun massacres” with the return of the 1994 federal assault weapons ban, said Louis Klarevas of the University of Massachusetts at Boston.

For his 2016 book “Rampage Nation,” Klarevas collected data on every gun massacre — which he defines as six or more people shot and killed — for the 50 years before 2016. His aim was to see whether there was any change in the number of gun massacres while the 10-year federal ban on assault weapons was in place.

He calls the results “staggering.” Compared with the 10-year period before the ban, the number of gun massacres during the ban period fell by 37 percent, and the number of people dying from gun massacres fell by 43 percent. But after the ban lapsed in 2004, the numbers shot up again — an astonishing 183 percent increase in massacres and a 239 percent increase in massacre deaths.

Klarevas says that the key provision of the assault weapons bill was a ban on high-capacity magazines capable of holding more than 10 rounds. “We have found that when large capacity mags are regulated, you get drastic drops in both the incidence of gun massacres and the fatality rate of gun massacres.”

The opinion is shared among many researchers who study gun violence for a living. In 2016, for instance, the New York Times asked 32 gun policy experts to rate the effectiveness of a variety of policy changes to prevent mass shootings. The roster of experts included violence prevention researchers like Harvard's David Hemenway, as well as more ideologically driven gun rights advocates like John Lott.

On a scale of effectiveness ranging from 1 (not effective) to 10 (highly effective), the expert panel gave an average score of 6.8 to both an assault weapons ban and a ban on high-capacity magazines, the highest ratings among the nearly 30 policies surveyed.

The killers in recent incidents like Las Vegas, Orlando and Sutherland Springs were each able to walk into a gun shop in the days and months before their attacks, and legally purchase their assault weapons and magazines after passing a standard background check. Under an assault weapons ban, that wouldn't be possible.

Supporters of an assault weapons ban, like Sen. Dianne Feinstein (D-Calif.), say that the goal of the bans is to prevent horrific mass shooting incidents, not stop the run-of-the-mill gun violence that kills dozens of Americans each day. Feinstein, along with 22 Democratic colleagues, introduced an assault weapons ban in the Senate after the Sutherland Springs shooting in Texas.

“This bill won’t stop every mass shooting, but it will begin removing these weapons of war from our streets,” Feinstein said in a statement. “Yes, it will be a long process to reduce the massive supply of these assault weapons in our country, but we’ve got to start somewhere.”

Feinstein's bill would ban 205 specific “military-style assault weapons” by name, and it more broadly bans firearms containing a detachable magazine and one or more “military characteristics,” including “a pistol grip, a forward grip, a barrel shroud, a threaded barrel or a folding or telescoping stock.” Current owners would be allowed to keep their existing weapons.

Feinstein's bill would also ban high-capacity magazines capable of holding more than 10 rounds of ammunition.

A number of surveys show that bans on assault weapons and high-capacity magazines are popular among the general public. A 2017 Pew Research Center poll found that 68 percent of adults favor banning assault weapons, and 65 percent support a ban on high-capacity magazines.

In recent years congressional Republicans have been more focused on expanding access to guns, rather than limiting it. In December the House passed a measure that would allow gun owners with concealed carry permits in one state to carry their weapons in every other state.

The experts polled by the New York Times in 2016 rated that as the least effective measure, by far, for dealing with mass shootings.

Corrections: An earlier version of this piece mis-stated the number of rounds held in a "high-capacity" magazine. It is more than 10 rounds, not 10 or more rounds.

Additionally, the percent drop in gun massacre deaths while the 1994 assault weapons ban was in place was 43 percent, not 49 percent.

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Christopher IngrahamChristopher Ingraham writes about all things data. He previously worked at the Brookings Institution and the Pew Research Center. Follow